logstash is a tool for managing events and logs. You can use it to collect logs, parse them, and store them for later use (like, for searching). Speaking of searching, logstash comes with a web interface for searching and drilling into all of your logs.
Part of the ElasticSearch family. ES not required, as output can be sent to any destination you want, such as statsd (which in its turn can flush the data to graphite in order to visualize it).